This invention relates to keyswitches and more particularly to keyswitches exhibiting a variable capacitance. Keyswitches are used in a wide variety of applications in the prior art, such as control circuits, keyboards for typewriters, calculators, computers and the like. The switches generally are classified according to the phenomenon relied upon to indicate activations--resistive, inductive, magnetic or capacitive.
Although capacitive keyswitches known in the prior art are somewhat simple in construction and immune to many of the problems of the contact and inductive switches, capacitive key switches of the prior art do not generally have a large variation (one order of magnitude or greater) in capacitance upon actuation. Furthermore, the capacitance type keyswitches of the prior art are particularly susceptible to environmental contamination from small particles such as eraser particles, lint and liquid spillage. Also, the capacitive keyswitches of the prior art generally have a low hysteresis and are quite sensitive to small changes in movement of the switch plunger.
One of the principal objects of this invention is to provide a reliable capacitive keyswitch that is self-cleaning and exhibits a linear capacitance change of a substantial magnitude.
An additional object is to provide such a capacitive keyswitch that additionally has a substantial capacitance hysteresis to enable the threshold values to be adjusted depending on the desired application.
A further object of this invention is to provide a new capacitive keyswitch that, in addition to the other advantages, has sufficient economy of space to easily accommodate lamps and tactile feel features.
These and other objects and advantages of this invention will become apparent upon reading the following detailed description of a preferred embodiment. Only the claims at the conclusion of the specification are intended to limit the scope of this invention.